The present invention generally relates to optical switching arrangements and more particularly, to arrangements of optical switching units for selectively manipulating optical signals from input and add ports to output and drop ports.
Traditionally, signals within telecommunications and data communications networks have been exchanged by sending electrical signals via electrically conductive lines. An alternate mode of data exchange is the transmission of optical signals through optical fibers. Information is exchanged in the form of modulations of laser-produced light. Although the equipment for efficient generation and transmission of the optical signals is available, the design of optical switches for use in telecommunications and data communications networks is problematic. As a result, switching requirements within an optical network may be met by converting the optical signals to electrical signals at the inputs of a switching network, and then reconverting the electrical signals to optical signals at the outputs of the switching network.
One prior art switching matrix is an ADD/DROP multiplexor switch that includes ADD and DROP ports in addition to the input and output ports. The multiplexor switches are used in telecommunications applications in which signals are passed through a series of nodes. Each node can introduce additional signals and is able to extract those signals that identify that node as a target. For example, each node may be a switching facility of a long distance carrier that supports calls to and from a number of cities. Calls that originate in a city are introduced using ADD ports within the switching facility of that city. Alternatively, data and voice information for calls directed to a telephone supported by that switching facility are extracted via DROP ports. A known switching arrangement 42 that can be used as a rearrangeable ADD/DROP switch is shown in FIG. 1. The arrangement includes a 4xc3x974 matrix of optical switching units for selectively coupling any one of four input ports 44, 46, 48 and 50 to any one of four output ports 52,54,56 and 58. In FIG. 1, switching units 60,62,64, 66, are in a reflective state that is shown as having a bubble at the area of the intersection of input and output waveguides to that switching unit. The remaining twelve switching units are in the transmissive state, since there are no bubbles present at the intersections of the input and output waveguides to those switching units.
Optical fibers are connected to each of the input ports 44-50 and each of the output ports 52-58. An optical signal introduced at the input port 44 is reflected at the switching unit 62 and output via the output port 54. Similarly, an optical signal from the input port 46 will reflect at the switching unit 64 for output at the port 56. An optical signal from input port 48 reflects at the switching unit 66 for output via the port 58. Finally, an optical signal on port 50 is reflected to output port 52 by the switching unit 60. By selective manipulation of the bubbles within the various trenches, any one of the input ports can be connected to any one of the output ports.
The arrangement 42 includes four ADD ports 68,70,72 and 74. Each ADD port is uniquely associated with one of the output ports 52-58, since an optical signal that is introduced at one of the ADD ports can be directed only to its aligned output port. Thus, an optical signal on add port 68 can be directed to the output port 52 by changing the switching unit 60 to the transmissive state. This change to the transmissive state places the input port 50 in optical communication with a drop port 76. As the DROP port 76 maps only to the input port 50, the DROP port cannot be optically coupled to any other input or ADD port. Similarly, each one of three other drop ports 78, 80 and 82 uniquely maps with the input ports 44,46 and 48, respectively, with which the DROP port is linearly aligned.
There is limited flexibility with regard to introducing and extracting signals with the optical arrangement 42 of FIG. 1. What is needed is an optical switching arrangement with a high degree of flexibility with respect to channeling optical signals from input ports to drop ports and from add ports to output ports.
An optical ADD/DROP multiplexor switch has row and column waveguide segments, on a waveguide substrate, with ends that intersect trenches positioned in one of two patterns. In the first pattern, the trenches are positioned along the diagonal while in the second pattern, the trenches are positioned in a regular array. The row and column waveguide segments are in fixed relation and generally parallel to the surface of the waveguide substrate. A heater substrate has heaters aligned to the waveguide substrate in accordance with the trenches. A liquid, disposable within the trenches, is responsive to the heaters. The liquid has an index of refraction such that optical transmission from a first selected waveguide segment to a second waveguide segment is determined by presence of the liquid within the trenches.
This configuration of the optical ADD/DROP multiplexor switch allows complete rearrangement of IN ports to DROP ports and ADD ports to OUT ports. The multiplexor switches may be cascaded such that the number of input and output ports may be increased while the number of switched ADD and DROP fibers are constant.